The present invention relates to a suspension control apparatus and a vehicle control apparatus, which are mounted to, for example, a vehicle such as a four-wheel automobile so as to be suitably used for damping the vibrations of the vehicle.
In general, a suspension control apparatus is mounted to a vehicle such as an automobile as described in, for example, Japanese Patent Application Laid-open No. 2003-11635. The suspension control apparatus includes a damping-force adjustable shock absorber provided between a vehicle-body side and each axle side. A damping-force characteristic obtained by the shock absorber is variably controlled according to a vehicle attitude which is changed along with a braking operation of a brake or the like.
The above-mentioned type of suspension control apparatus of the prior art is used in combination with a vehicle stability control apparatus to perform control for variably switching the damping-force characteristic, in order to reduce a change in vehicle attitude generated along with, for example, a steering operation and the braking operation of the vehicle so as to improve running stability. Specifically, the control is performed so that the damping-force characteristic of the shock absorber is set to a soft side during an extension stroke and is set to a hard side during a compression stroke on the side of a wheel to be braked, to which the braking force is to be applied, and the damping-force characteristic of the shock absorber is set to the hard side during the extension stroke and is set to the soft side during the compression stroke on the side of a wheel which is not to be braked, to which the braking force is not applied. As a result, a wheel load of the wheel to be braked is increased transiently.
The inventors of the present invention focused attention on the wheel load of the wheel during the compression stroke in the suspension control apparatus of the prior art and found that a maximum amount of increase in wheel load was reduced although a response to increase the wheel load was rapid when the damping force was set to the hard side as compared with the case where the damping force was set to the soft side. Moreover, the inventors of the present invention also focused attention on the wheel load of the wheel during the extension stroke and found that a maximum amount of wheel-load loss (reduction in wheel load) was reduced although a response to reduce the wheel load was rapid when the damping force was set to the hard side as compared with the damping force was set to the soft side.
Therefore, if the responsiveness to increase or lose the wheel load is improved for the wheel load during one of the extension stroke and the compression stroke, the maximum amount of increase or loss in wheel load is reduced. Therefore, the responsiveness and the maximum amount cannot be both improved at the same time. On the other hand, if the responsiveness is lowered, the maximum amount is increased. Therefore, the responsiveness and the maximum amount cannot be both reduced at the same time. Thus, it is found that the suspension control apparatus of the prior art has a problem in that only any one of the responsiveness and the maximum amount can be improved or reduced during any of the compression stroke and the extension stroke of the shock absorber.